Smooth patterns were written into PMGI electron-beam resist using electron-beam lithography on BK7 blank concave mirror substrates, resulting in aspheric optics with sag as large as 4 µm. Interference microscope measurements revealed that the fabricated optics had height accuracy of 10 nm. These optics were designed for flattop mode shaping in laser resonators. Excellent performance of these optics has been demonstrated by testing them as fixed phase-conjugate mirrors outside laser resonators, as well as mode-shaping mirrors within laser resonators.
An extended-cavity resonator with an aspheric third mirror aligned collinear to a standing-wave two-mirror resonator is studied. A number of benefits of this new cavity design such as improved mode selectivity and mode shaping were predicted by simulation. An experiment was performed with a Nd:YVO4 laser system. With an optimized aspheric third mirror, this three-mirror solid-state laser has an experimentally measured modal discrimination of 1.43 and oscillates in the designed fundamental Gaussian mode. The M2 of the cavity mode was measured to be 1.02. Applications of aspheric feedback mirrors in other advanced laser resonators are also briefly discussed.